This inventions relates to welding equipment, and more particularly to purge blocks for use in establishing a localized inert atmosphere inside two abutting pipe or tubing sections in the region of a desired weld joint, and to methods for using such purge blocks.
It is conventional in TIG welding and some other welding methods to establish an inert atmosphere inside two abutting pipe or tubing sections in the region of a desired weld joint. It is also conventional to establish an inert atmosphere on the outside of the pipe sections in the region of the desired weld joint, and weld heads are commercially available for establishing this external inert atmosphere as well as performing the welding operation. Without an inert atmosphere, the interior surface of the welded joint is subject to oxidation, other impurities and incomplete fusion of the pipe edges, particularly in the case of stainless steel pipe.
A common practice in the field involves filling an entire pipe line with a protective gas, such as argon, and, typically, providing a continuous flow of argon gas throughout the welding operation. A recognized drawback of this practice is that it consumes a large amount of argon and is therefore more costly than desired.
A known alternative to the above technique involves the use of purge blocks, dams or plugs, which, in one way or another, establish a localized inert atmosphere at the interior surface of a desired weld joint. Numerous such devices have been developed over the last fifty years, as exemplified by the following U.S. patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,179,176 Dunn Nov. 7, 1939 2,496,188 Wiese Jan. 31, 1950 2,787,699 Jessen Apr. 2, 1957 2,802,092 Hauck Aug. 6, 1957 2,819,517 Pursell Jan. 14, 1958 3,194,466 Davis Jul. 13, 1965 3,194,936 Rohrberg et al. Jul. 13, 1965 3,292,254 Sloan Dec. 20, 1966 3,736,400 Spiegel et al. May 29, 1973 4,278,864 De Facci et al. Jul. 14, 1981 4,828,160 Sundholm May 9, 1989 4,931,612 Belleride et al. Jun. 5, 1990 ______________________________________
Perhaps the most basic technique for localizing the inert atmosphere is to plug both exposed ends of the pipes or tubes to be welded, e.g., as shown in the patent to Jessen. Similarly, some devices consist essentially of separate dams, baffles or other seals which are either removable (Hauck, Sloan, De Facci et al. and Belleride et al.), combustible (Pursell) or water soluble (Spiegel et al.).
A number of devices employ either separate or interconnected inflatable plugs or seals, some of which have been designed to accommodate a number of pipe sizes. See, for example, the patents to Hauck, Davis, Sloan, Sundholm, and Belleride et al. Davis indicates that sealing tubes having a variety of outer diameters may be interchangeably mounted upon supply tubes to accommodate pipes of varied sizes. An extra source of pressure, e.g., air pressure, is commonly required for inflation of such devices, and there is a risk of damage to or rupture of the inflatable members in such devices due to heat generated in the welding operation, in the absence of additional protective design features for the inflatable members, such as shown in the patent to Sundholm, and/or careful placement of such devices prior to welding. Inflatable seals tend to be damaged in particular by a hot weld joint as they are moved past the joint after welding.
The known purge blocks in which seals on opposite ends of a spacer rod or tube are not inflatable, e.g., those in the patents to Dunn, Wiese and Rohrberg et al., do not adequately accommodate more than one pipe size, or are otherwise deficient in some respect. A set of complete tools of different sizes is normally required in welding applications involving different pipe sizes.
For many applications, it is adequate to manually place a purge block in the position for use, either with the aid of a tensioning element such as a wire, cable or the like, or with the aid of a rigid element such as a rod or pipe. Various techniques for moving such devices inside pipes are disclosed, for example, in the patents to Sundholm and Sloan. While such techniques are often adequate for a given application, they are sometimes cumbersome and not as convenient as desired.